Methods of power overload control in communication systems

ABSTRACT

Methods of providing power overload control in a communication system having a least one base station serving one or more users of at least one cell are described which may avoid an overload condition in the system. In one aspect, a target signal-to-interference ratio (SIR target ) may be controlled for inner loop power control implemented by the base station, so as to maintain the loading of the communication system below an overload condition. In another aspect, a target block error rate (BLER target ) may be controlled for outer loop power control implemented by the base station, so as to maintain the loading of communication system below an overload condition.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is generally related to power overload control incommunication systems.

2. Description of the Related Art

Third generation (3G) wireless communication systems such asCode-Division-Multiple-Access (CDMA) networks and Universal MobileTelecommunication Systems (UMTS) typically may include a plurality ofmobiles having transceivers communicating with transceivers of servingbase stations. Each mobile transceiver may include a transmitter and areceiver which communicate with a corresponding base station receiver ortransmitter via one or more links. A link typically may comprise aplurality of communication channels such as signalling channels andtraffic channels, for example. Traffic channels are communicationchannels through which users convey (i.e., transmit and/or receive) userinformation. Signalling channels may be used by the system equipment toconvey signaling information used to manage, operate and otherwisecontrol the system. The system equipment, which may be typically owned,maintained and operated by a service provider, may include various knownradio and processing equipment used in communication systems. The systemequipment along with user equipment (UE), e.g., mobiles, generate andreceive the signaling information.

Communication signals transmitted and received via communication linksmay often be distorted by various anomalies that exist in thecommunication channels. These channel anomalies may cause the signals tobe received erroneously. For example, channel anomalies such as pathloss, Rayleigh fading, frequency translation and phase jitter may oftencause the signals to lose power, so that a signal is received at asignificantly lower power level than it was transmitted. As a result,signals adversely affected by channel anomalies may often be receivedwith errors. One way of preventing errors from occurring, or at least toreduce the likelihood of errors occurring, is by applying power controltechniques to these communication systems.

In general, a power control algorithm may be performed at a basestation. In looking at a signal received from a mobile, if the signallooks weak (e.g., based on detected frame error rate (FER), forexample), the base station may send a command to either increase ordecrease mobile station transmit power. For example, a comfortable levelof quality in a voice system may be possible with a FER of approximately1%. If FER is much less than (<<) 1%, the mobile station may be wastingpower, so the power control algorithm implemented at the base stationmay send commands to the mobile requesting the mobile to reduce thetransmit power. For FER much greater than (>>)1%, the level of qualitymay be degraded, so the base station may send a command to the mobile tobring the mobile transmit power up in order to restore quality.

Typically, in order to effect power control at the base station, twopower control loops may be utilized, which together provide what isreferred to as ‘closed-loop power control’: inner loop power control andouter loop power control. In an exemplary CDMA communication system, forexample, an inner loop power control algorithm (‘inner loop’ or ‘fastpower control’), which may operate at a speed of 800 Hz, for example),may be used to adjust the power at the transmitter. Thus, a base stationmeasures a received signal to noise ratio (E_(b)/N_(t)), also known as asignal to interference ratio (SIR), and compares the SIR value to athreshold. The threshold may be used by the inner loop to determine aspecified quality of service (QoS) for power control. If the receivedSIR is too high (e.g., above the threshold), the base stationtransmitter may send a down power command to the mobile station, andvice versa where measured SIR is too low.

QoS may be representative of a number of different service requirements.For example, QoS may be indicative of providing guaranteed performance(e.g., such as a minimum or maximum data network throughput, a minimumdelay requirement, a packet loss rate, and/or a packet download time,etc.) in a given network such as UMTS. A system or network such as aUMTS or CDMA system may be designed to support several quality ofservice (QoS) levels to allow efficient transfer of non real-timetraffic (e.g., intermittent and/or bursty data transfers, occasionaltransmission of large volumes of data) and real-time traffic (e.g.voice, video), etc.

However, a communication path between base station and a mobile stationis not often line of sight (LOS), and may be constantly changing due tothe motion of the mobile station, or due to the mobile station'ssurroundings. For example, SIR changes may be caused by fast fading(like Rayleigh or Ricean fading), by shadowing (log-normal fading)and/or by changes in the interference level. Ideally, the received SIRshould remain constant to enable a good reception of the reverse linksignal (from the mobile to base station) without wasting transmit powerat the mobile station.

Thus, the radio channel conditions between the base station and a mobilemay be constantly changing. As the radio conditions change, thethreshold may be adjusted in order to maintain the QoS of the radiolink. The system that performs the function of adjusting the threshold(e.g., setting and adjusting the set point of the threshold) is referredto as the outer loop power control (‘outer loop’ or ‘slow powercontrol’). Together with the inner loop, the outer loop forms the closedloop power control.

Outer loop power control may be designed to control the current linkquality in terms of a bit-error rate (BER) or a block error rate (BLER),depending on requirements of the radio bearer service. Although the SIRis controlled by the inner loop power control, the received link qualitymay still change. As discussed above, these changes may be caused byvariations in the multi-path delay profile (typical urban, hillyterrain, etc.), alterations in the speed of the mobile and/ormodifications in the interference characteristics. The outer loop powercontrol thus may adapt a ‘target SIR’ of the inner loop (such as byadjusting the set point of the threshold) so that the required linkquality may be achieved.

In CDMA systems such as UMTS, there is thus a need for a power controlmechanism or algorithm to overcome path loss effects, and to balance thequality of service (QoS) between the various user services. However, incertain situations, a CDMA system may become overloaded.

FIG. 1 is a graph to illustrate the overload problem in communicationsystems such as UMTS. Referring to FIG. 1, as load reaches 100%, theinterference and transmit power for each mobile user may rapidlyincrease. In the high-load region, power control may not be effective,leading to unstable operation of the network. In a worst case scenario,a transmit power limit may have been reached, which could possibly leadto a drop of the connection, due to loss of synchronization betweenmobile and base station. To prevent an occurrence of this, efficientoverload control algorithms are desired in CDMA networks such as UMTS.

Conventional methods for addressing power overload events or situationsin wireless communication systems may include: (a) load or overloadcontrol; and (b) the aforementioned closed loop power control. Overloadcontrol may typically be employed in networks such as UMTS. Referringagain to FIG. 1, it is desirable that the right-most region of loadingshould be avoided, because at this point, the network or system maybecome unstable due to a rapid increase in both the interference andtransmit power. In FIG. 1, the region to be avoided may thus be referredto as an ‘outage area’.

In general, the following conventional methods may be employed toaddress the overload control problem in CDMA networks. One technique isreferred to as Call Admission Control (CAC). CAC functionality attemptsto avoid an overload situation by controlling the access of new users tothe network or system. The basic CAC functionality thus operates so asto not admit (i.e. block) a new user into the system, if the loadbecomes greater than a given threshold (thr_(admit)), as illustrated inFIG. 1, for example.

Another conventional method addressing overload may be referred to as‘congestion control’ (ConC). Even with a properly functioning CACroutine, a wireless communication system may become overloaded due tothe mobility of mobile users in the system. In such a case, ConCfunctionality may facilitate overcoming the overload situation.Referring again to FIG. 1, and in general, ConC methodology mayinterrupt (i.e. drop) an existing connection, if the load exceeds asecond given threshold (thr_(drop)). The thr_(drop) threshold typicallymay be set to a greater value then thr_(admit). Accordingly, use of theabove overload control methods (CAC and/or ConC) may lead to arelatively harsh reaction for users in a UMTS or CDMA system, if thesystem is in an overload situation.

Another radio resource management function related to overload controlmay be closed loop power control. Power control (PC) algorithmsimplemented at the base station may control the setting of the transmitpower in order to (a) maintain system QoS within required limits, e.g.,data rate, delay, BLER, etc.; and (b) to reduce and/or minimizeinterference, i.e., overall power consumption. PC may addresspropagation effects, like path loss (near-far-problem), shadowing(log-normal-fading) and fast fading (Rayleigh-fading, Ricean-fading), aswell as the impact of the environment (delay spread, UE speed, etc.) onthe wireless communication system.

FIG. 2 illustrates a block diagram of conventional closed loop powercontrol (CLPC) in a base station transceiver of a wireless communicationsystem. As discussed above, CLPC may include inner loop power control(ILPC) and outer loop power control (OLPC). As shown in FIG. 2, there isshown a block diagram of a transmitter side 210 of a user such as a UEand a receiver side 220 of a base station transceiver (hereafter theterms ‘base station’ and ‘NodeB’ may be occasionally interchanged).

The ILPC controls the transmit power settings of the transmitter side210 in order to achieve a desired or given SIR_(target), which has beenadjusted by the OLPC. Referring to FIG. 2, the basic function of ILPCmay be as follows. At the receiver side 220 of the NodeB, the SIR of agiven UE may be estimated (at 225) from a signal 222 received viareceiver 221. The received signal 222 may be compared againstSIR_(target) at element 225. Based on the comparison, transmit powercontrol (TPC) commands 226 may be generated. For example, ifSIR<SIR_(target), the ILPC of a given NodeB may generate a ‘power up’command to the UE that it is serving; if SIR>=SIR_(target), the ILPC ofa given NodeB may generate a ‘power down’ command to the UE.

The TPCs 226 may be multiplexed by a suitable MUX 227 into a data stream211 sent to the associated transmitting side 210 of the UE. Thetransmitter side 210 extracts the TPC commands 226 from the associateddata stream 211 at a suitable DEMUX 212. The transmitter side 210 mayadjust the transmit power of a power amplifier (PA) 217 therein based onthe extracted TPC commands received from DEMUX 212 via line 216. Forexample, when a power up command has been received from receiver side220, the transmit power of the UE may be increased by a given amount;after reception of a power down command, the transmit power may bedecreased by a given amount. ILPC is thus a closed loop between thetransmitter side 210 of the UE and receiver side 220 of the NodeB.

The OLPC controls the SIR_(target) setting (threshold) for ILPC in orderto fulfill the QoS requirement of the service, which may be given, forexample, by a certain BLER_(target) 230. Referring to FIG. 2, the basicfunction of OLPC may be as follows. Within the receiver side 220, theQoS of the service (e.g. the BLER) may be estimated (at 228) from thedecoded signal 224 (decoded by decoder 223) and compared against a QoStarget (e.g. given by BLER_(target)). An adjusted SIR_(target) for ILPCmay be determined (see line 229) based on the comparison at 228. Forexample, when BLER>BLER_(target), OLPC increases SIR_(target), and whenBLER<=BLER_(target), OLPC decreases SIR_(target). The revisedSIR_(target) (threshold) may be provided to ILPC. OLPC is also a closedloop, which primarily runs within the receiver side 220 of the NodeB.

In the uplink (‘reverse link’, mobile to base station) power control isperformed for each mobile user, separately, while in the downlink(‘forward link’, base station to mobile) power control runs per physicalchannel. In current realizations, no specific power control action isperformed when a power overload situation occurs. In an overloadsituation, conventional power control increases the transmit power tothe transmit power limit, even if the desired or target BLER has not yetbeen reached or met. This may lead to unexpected droppings of existingconnections, as the synchronization between transmitter and receiver hasbeen lost.

FIG. 3 illustrates a conventional arrangement for uplink power controlin a wireless communication system. System 300 may be embodied as a UMTSTerrestrial Radio Access Network (UTRAN) 300, for example. UTRAN 300 mayinclude cell sites, called Node Bs 310 (base stations), which may serveone or more UEs 315, generally using a Uu interface protocol. A Node B310 may contain radio transceivers that communicate, using lub protocol,with radio network controllers (RNCs) 320 and 325. Here, RNCs are shownas the controlling, or serving RNC (SRNC) 320 and a drift RNC (DRNC) 325of the UTRAN 300. The SRNC 320 and DRNC 325 may communicate with eachother using an lur protocol, for example.

UTRAN 300 may also interface with one or more core networks (CNs) 340(only one being shown in FIG. 3 for simplicity). Although not shown forreasons of brevity, CN 340 may include mobile switching centers (MSCs),one or more Serving GPRS Support Nodes (SGSNS) and one or more GatewayGPRS serving/support nodes (GGSNs). SGSNs and GGSNs are gateways toexternal networks (not shown). In general in UMTS, SGSNs and GGSNs mayexchange packets with mobile stations over the UTRAN 300, and may alsoexchange packets with other internet protocol (IP) networks, referred toherein as packet data networks (PDNs). External networks may includevarious circuit networks such as a Packet Switched Telephone Network(PSTN) or an Integrated Service Digital Network (ISDN) and PDNs.

As shown in FIG. 3, UTRAN 300 may be linked to CN 340 via suitable Iuinterfaces such as Iu cs and Iu ps (not shown for clarity), for example.Alternatively, UTRAN 300 may be linked to the CN 340 via back-haulfacilities (not shown) such as T1/E1, STM-x, etc., for example. Ics,short for Interface Unit (Circuit Switched) interface, is the interfacein UMTS which links the RNC with a MSC. Ips, short for Interface Unit(Packet Switched) interface, is the interface in UMTS which links theRNC with a SGSN.

According to the 3GPP UMTS standard such as 3GPP TS 25.401, V6.2.0(2003-12), entitled “UTRAN overall description), the different uplink PCfunctions may be located in different network entities. FIG. 3illustrates an example for the location of uplink control functions in acase of soft handoff between NodeBs 310. Soft handover is a callconfiguration whereby the UE is simultaneously connected to more thanone cell. In this example, the UE 315 is connected to different NodeBs310 and different RNCs 320 and 325, with each NodeB 310 connected to anassociated controlling RNC 320/325 via the Iub interface. If thecontrolling RNCs are different for the NodeB 310 involved in softhandoff, one RNC takes the part of SRNC 320 for controlling theconnection, while the other acts as a DRNC 325. As shown, UE 315 dataand control flows between RNCs 320/325 may be transmitted via the Iurlogical interface.

Conventionally, the ILPC function is located in each NodeB 310, thusproviding separate ILPC loops between a given UE 315 and each NodeB 310.The 3GPP UMTS standard provides specified rules for the UE 315, in acase where the TPC commands from these separate loops are in conflict.The frame selector 322 may be adapted to select the most reliable datastream between the different uplink soft handover paths that reach theSRNC 320, and may be located in the SRNC 320. Also, OLPC functionality324 may typically also be located in SRNC 320, as shown in FIG. 3, forexample.

Accordingly, conventional power control implementations do not presentan efficient way of addressing and handling overload conditions,particularly in the uplink. For example, for a short term overload, suchas a few tenths of a second, for example, any action by the PC may betoo harsh, adversely affecting users by blocking or dropping users ascurrently done by conventional overload control algorithms such as CACand/or ConC.

Further, in the case where no action is done in response to an overloadsituation, the power control loops for a given number of users may reachcorresponding limits, which could lead to unexpected and uncontrolledperformance degradation for the service. In the extreme case,synchronization between a given UE 315 and its serving NodeB 310 may belost and the call dropped.

SUMMARY OF THE INVENTION

An exemplary embodiment of the present invention is directed to a methodof providing power overload control in a communication system having aleast one base station serving one or more users of at least one cell.In the method, a target signal-to-interference ratio (SIR_(target)) maybe controlled for inner loop power control implemented by the basestation, so as to maintain the loading of the communication system belowan overload condition.

Another exemplary embodiment of the present invention is directed to amethod of providing power overload control in a communication systemhaving a least one base station serving one or more users of at leastone cell. In the method, a target block error rate (BLER_(target)) maybe controlled for outer loop power control implemented by the basestation, so as to maintain the loading of communication system below anoverload condition.

BRIEF DESCRIPTION OF THE DRAWINGS

The exemplary embodiments of the present invention will become morefully understood from the detailed description given herein below andthe accompanying drawings, wherein like elements are represented by likereference numerals, which are given by way of illustration only and thusare not limitative of the exemplary embodiments of the presentinvention.

FIG. 1 is a graph to illustrate the overload problem in communicationsystems such as UMTS.

FIG. 2 illustrates a block diagram of conventional closed loop powercontrol (CLPC) in a base station transceiver of a wireless communicationsystem.

FIG. 3 illustrates a conventional arrangement for uplink power controlin a wireless communication system.

FIG. 4 is a flow diagram illustrating a method for power overloadcontrol in a communication system in accordance with an exemplaryembodiment of the present invention.

FIG. 5 is a flow diagram illustrating a method for power overloadcontrol in a communication system in accordance with another exemplaryembodiment of the present invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Although the principles of the exemplary embodiments of the presentinvention are particularly well-suited for wireless communicationsystems based on UMTS technologies, standards and techniques, and willbe described in this exemplary context, it should be noted that theexemplary embodiments shown and described herein are meant to beillustrative only and not limiting in any way. For example, theexemplary embodiments of the present invention is also applicable to thewell-known IS-95, IS 2000 and/or CDMA 2000 technologies forcommunication systems. As such, various modifications will be apparentto those skilled in the art for application to other wirelesscommunication systems and are contemplated by the teachings herein.

Additionally where used below, the term ‘user equipment’ (UE) may beconsidered synonymous to a mobile station, mobile, mobile user,subscriber, user, remote station, access terminal, etc., and maydescribe a remote user of wireless resources in a wireless communicationnetwork. The term ‘NodeB’ may be considered synonymous to a base stationor base transceiver station (BTS), and may describe equipment thatprovides data and/or voice connectivity between a network and one ormore UEs. A system or network (such as an access network) may includeone or more base stations.

Exemplary embodiments of the present invention may be directed tomethods of power overload control in the uplink, although the exemplarymethods may be applicable to addressing an overload situation in thedownlink, as would be evident to one having ordinary skill in the art.The exemplary methodology described hereafter may be applicable in lieuof, and/or in addition to, conventional load control methodologies suchas Call Admission Control (CAC) and Congestion Control (ConC), forexample.

In general, the exemplary methodologies described herein forimplementing power overload control in wireless communication systemsmay be based on a principle that an overload situation may occur for afinite time in communication systems supporting a specific load that isbelow a maximum load limit. Therefore, it may be desirable to restrictthe QoS for users served by the system in terms of, e.g., increasing theBLER for a finite period, instead of implementing a more drastic actionsuch as blocking a new user or dropping an existing user, as is done inconventional load control methodologies such as CAC and ConC.

As will be described in further detail hereafter, in an exemplaryembodiment, a target signal-to-interference ratio (SIR_(target)) forILPC may be controlled so as to maintain the communication system belowan overload condition. This may be done based on knowledge that transmitpower, and hence overall loading of a system, may depend directly on anadjusted SIR_(target) for inner loop power control.

As will be described in further detail in another exemplary embodiment,the target block error rate (BLER_(target)) for ILPC may be adjustedbased on the system load at a given instant. Accordingly, anotherexemplary embodiment is directed to a method for power overload controlin which SIR_(target) for ILPC may depend on BLER_(target), via OLPCfunctionality.

FIG. 4 is a flow diagram illustrating a method for power overloadcontrol in a communication system in accordance with an exemplaryembodiment of the present invention. In general, FIG. 4 illustrates amethod for overload control that may be based on controlling theSIR_(target) for inner loop power control.

Referring to FIG. 4, a ‘power overload control loop’ 400 may beimplemented in addition to ILPC. In a CDMA or UMTS system, theSIR_(target), which is controlled by the ILPC, may have an influentialimpact on the interference, and hence loading, of a given cell (where acell may include one or more UEs served by a NodeB).

On one hand, lowering the SIR_(target) may also reduce the load of thecell, and therefore may facilitate overcoming a temporary overloadsituation. On the other hand, a lower SIR_(target) may also degrade BLERperformance of the communication system. Hence, the QoS may also bedegraded during an overload period or situation. The exemplarymethodologies described herein account for the trade-off between theability to overcome an overload situation and the potential degradationto system performance.

Referring to FIG. 4, a NodeB may regularly estimate (S410) the currentloading of a given cell. In the uplink, this loading may be based on anoverall received interference. For example, the NodeB may monitor theload by measuring the cell interference level for a given cell it isserving. The estimated uplink load may be utilized by loop 400 in lieuof or in addition to other load control functionalities such as CAC andConC, for example. For the example of FIG. 4, load estimates for one ormore UEs in each cell may be reported by the serving NodeB to thecontrolling RNC of a network such as a UTRAN, for example.

In order to detect an overload situation at the NodeB, the estimatedload may be compared (S420) against a given overload threshold(thr_(overload)). Based on the comparison, a SIR scaling factor(fac_(SIR)) may be adjusted (S430). For example, if estimated load isequal to or exceeds (>=) thr_(overload), fac_(SIR) may be reduced by agiven amount (i.e., by a percentage or set value that does not lower thefac_(SIR) below a given minimum value (min(fac_(SIR))). If the estimatedload is less than (<) thr_(overload), the fac_(SIR) may be raised onincremented by a given amount (i.e., by a percentage or set value thatdoes not raise the fac_(SIR) above a given maximum value(max(fac_(SIR))). In this example, max(fac_(SIR)) may be=1, although oneor ordinary skill in the art may use other values for max(fac_(SIR)),such as a fraction, decimal, integer other than 1 and the like.

In order to avoid instabilities when determining a target SIR, thescaling factor fac_(SIR) may be filtered (S440). For example, arelatively simple forgetting factor may be applied in accordance withexemplary expression (1):facs _(SIRave)(i)=(1−a)·fac _(SIRave)(i−1)+a·fac _(SIR)(i).  (1)In expression (1), fac_(SIRave(i)) may represent a current output valueafter filtering, fac_(SIRave(i-1)) may represent the previous outputvalue, ‘a’ may represent a filter coefficient, and fac_(SIR(i)) mayrepresent the current scaling factor value obtained from S430.

Based on the determination of fac_(SIRave(i)) in S440, a targetSIR_(target) for the ILPC may be adjusted (S450) as set forth inexemplary expression (2):SIR _(target) =SIR _(targetOLPC) ·fac _(SIRave)  (2)

In expression (2), SIR_(targetOLPC) represents the original target SIRas adjusted by OLPC. The revised value for SIR_(target) may thus beprovided (S460) to the ILPC implemented by the NodeB. If theSIR_(target) was lowered (as compared to the current SIR_(target)implemented by the ILPC methodology in the NodeB) due to the aboveiterations S410-S460, then the ILPC implemented at the NodeB may reducecommanded transmit power via the conventional operation, i.e., bysending a suitable power down command to the UE. Hence, the offered load(if approaching or at a power overload condition) may be reduced in anefficient manner. Further, information related to the impact of therevised SIR_(target) on system performance may be used (S470) todetermine a next load estimate at S410 at another time instant, forexample. The details of ILPC operations have been generally describedabove, thus a detailed description here is omitted for sake of brevity.

Accordingly, the exemplary methodology may be efficiently applied in theNodeB, where cell load information for deciding on SIR_(target) may beavailable, so that any latency between power overload control and ILPCmay be kept relatively low. In an effort to make the load reduction evenmore efficient, the power overload control loop shown in FIG. 4 may beemployed for all UEs of a cell or at least a group of UEs in that cell.In the case of soft handoff, only the SIR_(target) setting of the cellwhich is in overload is affected.

In the case where SIR_(target) is lower than SIR_(targetOLPC), withoutany further action the OLPC would increase SIR_(targetOLPC) againbecause the target quality, in terms of BLER_(target), for example,would not have been reached. This effect may be referred to as the ‘windup’ effect, which may pose a serious problem in CDMA systems such asUMTS.

To avoid the wind-up effect, the OLPC should be informed of the targetquality (BLER_(target)), so as to prevent the OLPC implemented by theNodeB from unnecessarily raising SIR_(targetOLPC). By applying thedistributed OLPC architecture and a suitable power control signallingmethod, such as is described in European Patent Application No.01309520.3 (published as EP1311076), to Charriere et al, filed Nov. 12,2001 and entitled “Control of the transmission power of a CMDA basedsystem”, this signalling may be inherently given. The contents ofEP1311076, as related to the described power control signaling method,are incorporated by reference herein.

The impact of certain given parameters of the power overload controlmethodology on system performance may be explained as follows. Theoverload threshold thr_(load) may directly provide the point of loadingto the NodeB, or in other words, the trigger at which the exemplarypower overload control methodology described herein should be initiated.The overload threshold thr_(load) should be adjusted according to themaximum allowable loading of the cell, which is given by an overloadthreshold thr_(CAC) for CAC and an overload threshold thr_(ConC) forConC, for example.

CAC and ConC functionality may still be needed to overcome—massiveoverload situations, especially if they last more than a few seconds,where power overload control may potentially lead to unacceptable BLERperformance for UEs of a given cell. A minimum bound such asmin(fac_(SIR)) may be used to adjust a worst allowable quality limit fora specific service, for example. The filter coefficient a described inexpression (1) may have a substantial impact on the dynamics of poweroverload control. Further, there may be a trade-off between the abilityto overcome the overload situation, and potential QoS degradation byadjusting one or more of the thr_(load), the min(fac_(SIR)) and thefilter coefficient a.

FIG. 5 is a flow diagram illustrating a method for power overloadcontrol in a communication system in accordance with another exemplaryembodiment of the present invention. In general, FIG. 5 illustratesoverload control that may be based on setting the BLER_(target) forouter loop power control. In CDMA systems, the BLER of a given servicemay have an influential impact on the transmit power, via the OLPC andILPC implemented at the NodeB, and hence, may substantially impactloading of a given cell.

Referring to FIG. 5, a NodeB may regularly estimate (S510) the currentloading of a given cell that one or more UEs are connected to. In theuplink, this loading may be based on an overall received interference.The estimated uplink load may be utilized in lieu of or in addition toother load control functionalities such as CAC and ConC, for example.For the example of FIG. 5, load estimates for one or more UEs in eachcell may be signalled by the serving NodeB to the controlling RNC of anetwork such as a UTRAN, for example.

The load estimated may be utilized to determine an adjustment (S520) tothe BLER_(target). To set or adjust the BLER_(target), the estimatedload may be divided into several areas (S521), with definedBLER_(target) settings for each area, depending on the requestedservice. In a simple example, two areas may be assumed, it beingunderstood that fewer or greater areas then two may be defined by onehaving ordinary skill in the art. Two exemplary load areas may bedefined as a ‘low load’ area and ‘high load’ area, for example. Eacharea may have a specified BLER_(target) setting, for example. Theassociation between the areas and the determination of an adjustment toBLER_(target) may be described as described below.

If the area is determined to be a low load area (output of S522 is YES),then assign BLER_(targetlow) (S523). If the area is determined to be ahigh load area (output of S524 is YES), then assign BLER_(targethigh)(S525). In an aspect, it may be desirable to setBLER_(targetlow)<BLER_(targethigh), since the load/power consumptiondecreases as the BLER target increases. The revised or adjusted valuefor BLER_(target), based on the area evaluated, may be provided (S530)to the OLPC implemented by the NodeB, as shown in FIG. 5.

The methodology described in FIG. 5 may be initiated at the beginning ofa new service for getting an initial BLER_(target), and/or during theexistence of a selected service by dynamically (i.e., in essentiallyreal time) updating BLER_(target). Because the end user perceivedperformance may be affected, it may be desirable to implement themethodology of FIG. 5 for only certain types of calls in a given cell.The decision as to which UE to submit to the methodology of FIG. 5 maybe based on the QoS requirement of the service or on some other priorityor parameter, for example. In the case of soft handoff, all links may beaffected from the new BLER_(target) setting.

The methodology as described in FIG. 5 may be efficiently applied in theRNC, where the quality information for the service, e.g. the BLER, maybe available due to the location of the frame selection function in UMTS(see frame selection function 322 in FIG. 3, for example). Furthermore,general load information (e.g., load information of adjacent cells)which may be used for determining an adjusted BLER_(target) setting, mayalso be available in the RNC. Due to the general long-term nature of theBLER_(target) adjustment, any latency between NodeB and RNC is notrelevant to BLER_(target) adjustment. The BLER_(target) adjustmentmethodology may be efficiently supported by the distributed OLPCarchitecture and power control signalling method, as described in EPApplication No. 01309520.3.

The exemplary embodiments may provide several benefits within the realmof power control in wireless communication systems. For example, theexemplary methodology described in FIG. 4 may efficiently address ashort term overload situation by temporarily lowering the SIR_(target)for the ILPC. This may avoid the need for more drastic measures such asblocking a new call or dropping an existing call, as implemented byconventional CAC and ConC functionalities. Additionally, by theselection of given parameters such as one or more of the thr_(load), themin(fac_(SIR)) and the filter coefficient a, the methodology asdescribed in FIG. 4 may achieve a desired trade-off between the abilityfor power overload control to overcome short term overload and QoSdegradation due to worsening BLER performance, in the case where theadjusted SIR_(target) results in a lower SIR_(target).

If the methodology of FIG. 4 is combined with existing overload controlmethods such a CAC and ConC, long or longer-term overload situations maybe overcome. In such a configuration, power overload control may betwo-fold: firstly, where overload is short in time, power overloadcontrol may temporarily reduce QoS without affecting the user(s).Secondly, and if due to any reason the overload situation become oflonger duration, CAC and ConC functionalities may be implemented toovercome a longer-term power overload situation by blocking or droppingcalls. However, it may be expected that with power overload control, thethresholds for overload events may be set higher than would be withoutthe enhanced overload control loop 400 of FIG. 4.

The methodology as described in FIG. 5 may provide a longer termadaptation of the QoS to the loading situation. If the load is lower, ahigher QoS (in terms of lower BLER_(target)) can be given to specificusers, than for higher loading, where larger BLER_(target) may be moreappropriate. Further, it is evident to one having ordinary skill in theart that the methodologies in FIGS. 4 and 5 may be combined to providean efficient mechanism for addressing and processing load fluctuationsby regulating the QoS of the requested service.

Moreover, although the methodology of FIG. 4 may be more suited for theuplink, because only in the uplink direction is a direct interface givento ILPC, the methodology of FIG. 5 may also be used in the downlink,because the OLPC targets for both directions may be set in the servingor controlling RNC of the UTRAN. Accordingly, the temporary reduction inquality may avoid unnecessary early dropping of calls. Hence, a highercapacity may be possible in the event of a power overload condition in acommunication system such as UMTS, in light of the above-describedmethods for power overload control.

The exemplary embodiments of the present invention being thus described,it will be obvious that the same may be varied in many ways. Forexample, the logical blocks in FIGS. 2-5 may be implemented in hardwareand/or software. The hardware/software implementations may include acombination of processor(s) and article(s) of manufacture. Thearticle(s) of manufacture may further include storage media,computer-readable media having code portions thereon that are read by aprocessor to perform the method, and executable computer program(s). Theexecutable computer program(s) may include instructions to perform thedescribed operations and the method. The computer executable(s) may alsobe provided as part of externally supplied propagated signals. Suchvariations are not to be regarded as a departure from the scope of theexemplary embodiments of the present invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. A method of performing power overload control in a communicationsystem, comprising: estimating a loading of one or more users of a givencell in the system based on a signal-to-interference ratio; comparingthe estimated load to a threshold; determining an adjustment to ascaling factor based on the comparison; filtering the scaling factor;and adjusting a target signal-to-interference ratio (SIR_(target)) tocontrol a power overload condition in the system based on the filteredscaling factor.
 2. The method of claim 1, wherein a power overloadcondition in the system is detected based on the comparison.
 3. Themethod of claim 1, wherein comparing includes evaluating the estimatedload against an overload threshold, and determining includes reducingthe scaling factor by a given amount, if the load estimate is equal toor exceeds the overload threshold.
 4. The method of claim 3, whereindetermining further includes incrementing the scaling factor by a givenamount, if the load estimate is less than the overload threshold.
 5. Themethod of claim 1, wherein the scaling factor is incremented or reducedbased on the comparison between a set minimum bound and a set maximumbound.
 6. The method of claim 1, wherein the filtering step furthercomprises: filtering the scaling factor based on a filtering coefficientto account for fluctuations in estimated load.
 7. The method of claim 6,wherein adjusting includes adjusting SIR_(target) for inner loop powercontrol as implemented by a base station serving the cell based on thefiltered scaling factor and a current SIR_(target) threshold set byouter loop power control that is implemented by the base station.
 8. Themethod of claim 1, wherein the adjusted SIR_(target) of all users of thecell or at least a group of users of the cell, for controlling the poweroverload condition is applicable to controlling an overload condition atone of the cell and network level.